Sorry, I forgot to include the most important difference between AMA, Dirt Late Models and other forms of motorsports to karting – Spectators.
Tracks can make their money on charging $10-20 per person to come and watch an event. AMA, they get thousandths of spectators, so plenty of revenue there. Oval tracks, most local programs can get anywhere from 100 t0 500 depending on the size of facility, weather, location, etc. 500 people at $20 a ticket is an easy $10,000. There is your purse for racing.
Karting, pit pass money goes toward paying the insurance, anywhere from $3-5 per pass, about the same goes to the track for their insurance program, and then the rest goes to the series/promoter to help pay costs, or to fund the trophy fund.
Is national karting expensive, yes, it can be when you include all the travel costs and equipment to be at the best it can be. Are promoters making million$ on hosting events. No, they are making decent living while taking the risk of promoting events.